Question

The dissociation constant of an acid HA is `1 xx 10^(-5)`. The pH of 0.1 molar solution of the acid will be
A. Five
B. Four
C. Three
D. One

Answer 1

Correct Answer - C
`HA hArr H^(+) + A^(-)`
`[H^(+)] = 0.1 M , [H^(+)]^(2) = K_(a) xx C`
`[H^(+)] = sqrt(K_(a) xx C) = sqrt(1 xx 10^(-5) xx 0.1) = sqrt(10^(-6))`
`[H^(+)] = 10^(-3)M, pH = 3`.